Magnetic core and coil assembly and terminal pad arrangement therefor



June 8, 1965 R. F. KUKLA 3,188,592

MAGNETIC coRE AND eon, ASSEMBLY AND TERMINAL PAD ARRANGEMENT THEREFOR Filed Oct. 11. 1961 4 Sheets-Sheet 1 & AHZZAV/W June 8, 1965 R. F. KUKLA MAGNETIC CORE AND COIL ASSEMBLY AND TERMINAL PAD ARRANGEMENT THEREFOR 4 Sheets-Sheet 2 Filed Oct. 11. 1961 June 8, 1965 R. F. KUKLA MAGNETIC CORE AND COIL ASSEMBLY AND TERMINAL PAD ARRANGEMENT THEREFOR 4 Sheets-Sheet 5 Filed Oct. 11. 1961.

R. F. KUKLA 3,188,592 MAGNETIC CORE AND COIL ASSEMBLY AND TERMINAL A June 8, 1 965 PAD ARRANGEMENT THEREFOR Filed 001?. 11, 1961 4 Sheets-Sheet 4 United States Patent O 3,188,592 MAGNETIC CORE AND COIL ASSEMBLY AND TERMINAL PAD ARRANGEMENT THEREFOR Robert F. Kukla, Danville, Ill., assignor to General Electric Company, a corporation of New York Filed Oct. 11, 1961, Ser. No. 144,411 4 Claims. (Cl. 336-192) This invention relates to magnetic core and coil assemblies and terminal pad arrangements. More particularly, it relates to such magnetic core and coil assemblies which are adaptable for use in ballasts for operating fluorescent lamps.

It is a common practice in the construction of ballasts to bring out the conductors from the coil of the ballast transformer to the top of the coil and to make connections with these. leads to a terminal pad attached to the coil. In the finishing operation, the coil conductors are positioned prior to soldering by twisting the conductor around the terminal. It will be appreciated that coils of ballast transformers, particularly the high voltage coils, are comprised of a fine gauge wire. Electrical connections must be made between these fine wire conductors and leads of heavier gauge wire such as the leads which are brought out from the ballast to the lamps and the power supply. It is the general practice in the industry to individually solder coil conductors and leads with a hand held soldering iron.

A number of diificulties have been experienced with the prior art practice and terminal pad arrangements. First of all, a frequent cause of ballast failures has been open circuits resulting from cold solder connections at the terminals. Where the fine wire coil conductors and leads are soldered on top of the coil, it is diflicult to determine whether or not the fine wire conductors and terminals being joine-d are suificiently heated to effect a good soldered connection. Also, it was found that the practice of twisting the fine wire conductors around a terminal Will often cause the conductor to break away.

In the shell type transformers commonly used in ballasts, the coi'ls are disposed on a center winding leg and extend outwardly thereof. Thus, the dimensions of the coil determine the height of the case in which the ballast is housed. Since the terminal pads are generally mounted on top of the coil, it will be appreciated that such prior art arrangements result in an increased height of the ballast case. Ballast case height is a critical factor in many ballast applications since the ballast is generally concealed by the fluorescent lamp fixture.

Another disadvantage of prior constructions is that a base insulation member located between the coil and case is required to insulate the terminals from the ballast case. The base insulation member covers the coil so that the connections will not touch the metallic base or cover plate of the ballast case. A base insulation member located over the coil and also the terminal pad located over the coil impair the heat transfer from the coil to surrounding environment. Efiicient heat transfer from the coils is an important consideration in the design of ballasts since overheating of the coils will eventually result in a failure of a ballast. It will be understood that the base of the ballast case is usually attached to the lamp fixture which serves as a heat sink for the heat energy generated in the ballast. In some prior art arrangements, the ballast transformer has been placed in the ballastcase in an upside down arrangement so that the terminal pads are disposed near the top of the ballast case and so that the other side of the coil can be disposed adjacent to the ballast base. Therefore, it is desirable to provide a terminal pad arrangement wherein both the top and the bottom sides of the coils can be disposed 3,188,592 Patented June 8, 1965 adjacent to the top and the base of the ballast case so that heat generated by the ballast transformer can be etficiently transferred therefrom.

From a manufacturing standpoint, it has been difficult not only to maintain the quality of solder connections made on terminal pads mounted on top of the coils but such an arrangement entails relatively expensive hand assembly operations. For this reason, it is desirable to provide a terminal pad arrangement for a ballast that is readily adaptable to more efficient manual assembly and to manufacturing operations that can be performed by machines.

Accordingly, it is a general object of this invention to provide an improved magnetic core and coil assembly.

Another object of this invention is to provide an improved electrical terminal pad arrangement for a magnetic core and coil assembly wherein fine conductors brought out from the coils and heavier external wire leads can be readily connected in circuit with the windings of the transformer.

It is still another object of this invention to provide an improved electrical terminal pad arrangement for a magnetic core and coil assembly which will not appreciably affect the height of the magnetic core and coil assembly.

A. further object of this invention is to provide an improved terminal arrangement for a ballast magnetic core and coil assembly wherein the soldering operation can be readily performed by mechanized techniques.

It is still a further object of the invention to provide an improved magnetic core and coil assembly for a ballast transformer whereby heat generated within the coils during operation is efliciently transferred therefrom.

These and other objects and advantages of the invention are achieved in a core and coil assembly having core clamps at each end thereof wherein at least one terminal pad is mounted on the core clamp. The terminals of the terminal pad are arranged so that they are aligned with the top side of the coil outwardly from above the core. Coil conductors brought out from the end of the coil may be either connected directly from the ends thereof to the terminals or may be passed over the top side of the coil and connected to the terminals, the terminal pad being attached to the core clamp and positioned thereon so that the terminals are aligned with the top side of the coil. Thus, the terminal pad arrangement does not to any appreciable extent add to the over-all height of the magnetic core and coil assembly and eliminates the need for mounting the terminal pads horizontally on the top side of the coil.

In another aspect of the invention, 1 have provided a terminal pad arrangement wherein the fine coil conductors and relatively heavy external leads are attached thereto in an overlying and an underlying arrangement, the fine coil conductors overlying the heavy external leads. The terminal pad includes a base portion formed of dielectric material and a plurality of terminals attached along a horizontal edge thereof. The terminals extend vertically from the base portion and the outer ends of the terminals extend downwardly to form a lead receiving window. A downwardly extending tongue is cut out from the terminal so that it is aligned with the lead receiving window and is adapted to grip the end of a lead inserted through the coil receiving window. The improved terminal pad arrangement of the invention makes it possible to position the relatively heavy leads which are to be connected to the terminals without adding to the height of the magnetic core and coil assembly. Thus, these leads are attached to the terminal in anunderlying relation therewith while the fine wire coil conductors are attached to the terminals in an overlying relation therewith. At least one tab extending upwardly and trans versely is formed on the terminal to position the fine I coil conductors on the terminal.

The subject matter which I regard as my invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be understood by referring to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a plan View of an unpotted ballast with the base or cover plate cut away to show a magnetic core and coil assembly embodying the invention;

FIG. 2 is a fragmentary perspective view of an end of themagnetic core and coil assembly of FIG. 1 illustrating the terminal pad arrangement with the conductor tabs in the open position;

FIG. 3 is a fragmentary perspective view of a core clamp and terminal pad illustrating the details of the terminal pad arrangement shown in FIG. 1 with the conductor tabs in the closed position;

FIG. 4 is another fragmentary perspective view, of a core clamp and terminal pad arrangement illustrating a modification of the terminal shown in FIG. 3;

FIG. 5 is a perspective view of a magnetic core and coil and terminal. in accordance with the invention illustrating how the coil conductors can be readily trimmed;

FIG. 6 is a perspective view of the magnetic core and coil assembly shown in FIG. 5 with the terminal bent upwardly in preparation for the soldering operation;

FIG. 7 is a perspective view of the terminal and transformer assembly as illustrated in FIG. 6 showing how the improved terminal pad arrangement readily permits the coil conductors to be simultaneously dip soldered;

FIG. 8 is an enlarged view of a terminal illustrating how a heavy external lead is connected to the terminal after the coil conductors have been soldered thereon;

FIG. 9 is a view of the terminal corresponding to the view shown in FIG. 8 illustrating how the terminal is bent so that the downwardly extending tongue formed thereon engages the end of the heavy lead; and

FIG. 10 is a perspective view of the magnetic core and coil assembly in accordance with the invention illustrating how the heavy leads are simultaneously soldered to the terminals.

Referring now in more detail to the drawings and more specifically to FIG. 1,. I have illustrated therein a ballast identified generally by the reference numeral 4. The ballast 4 includes a magnetic core and coil assembly or transformer 5, a capacitor 6, a ballast case 7 having a base or a cover plate 8, fine coil conductors 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18, and the relatively heavy external leads 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 and 29. The magnetic core and coil assembly 5 includes a pair of coils 3t), 31, a magnetic core comprised of a center winding leg 32 and yoke members 33, 34 disposed at each side of the center winding leg 32, core clamps 35, 36 and a pair of terminal pads 37, 38 mounted on the core clamps.

The coils 30, 31 are of conventional construction having layers of paper insulation between each of the winding layers and may include a plurality of windings such as one ormore secondary windings, a primary winding and filament heating windings. Only the outer wrappers of the coils 30, 31 are seen in view of FIG.']. since the particular coil construction does not constitute a part of this invention. Although I have shown coils 3t 31 which are of a type conventionally used in ballast transformers, it will be appreciated that the terminal pad arrangement of the invention is particularly adaptable to random Wound coils which do not have layer insulation.

In the magnetic core and coil assembly 5, I have employed shunts 40, 41 which are inserted between the coils 30, 31 to provide a linear or nonlinear reactance as may be desired. In ballast transformers where it is desirable to increase the leakage reactance of the transformer, this is accomplished by the inclusion of a high reluctance flux leakage path between the primary winding and the secondary winding which are included in the coils. Depending upon the particular design of the ballast transformer, the flux leakage path may be formed either through nonmagnetic material such as air or through magnetic mate rial such as the shunts 4t 41. Thus, in the exemplification of the invention illustrated in FIG. 1, the magnetic core and coil assembly 5, in addition to its transformer or voltage transformation function serves to limit the current flow in the ballast which is required because of the negative resistance characteristic of fluorescent lamps.

In accordance with the invention, I have mounted the terminal pads 37, 38 on each of the core clamps 35, 36. It will be seen that the fine coil conductors 9, 1t), 11, 12,13, 14, 15, 16, 17 and 18 are brought out from the ends of coils 30, 31 to the terminal pads 37, 38. As is best seen in FIG. 2, terminal pad 38 is provided with five terminals 42, 43, 44, 45 and 46. Both terminal pads 37, 38 are symmetrical in construction and are interchangeable. The number of terminals used will, of course, depend upon the number of connections to be made in the particular ballast circuit.

The terminal pad 38 has a U-shaped base portion 47 formed of a dielectric material, such as cardboard. It will be noted that the terminals 42, 43, 44, 45 and 46 are attached to the base portion 47 along the upper edge of the inverted U-shaped base portion 47 and are formed of a strip of conductive material. An inside edge of the base portion 44 abuts against a pair of tabs 48, 49. The clamp 36 includes a web portion and is vertically disposed adjacent to the end of the magnetic core and coil assembly 11. Thus, tabs 48', 49 firmly secure the base portion 47 against the web portion 50 in a vertically disposed position. This arrangement permits the terminal pad 38 to be accurately positioned with respect to the coils 30, 31.

. Further, it will be noted that each of the terminals 42, 43,

44, 45 and 46 are of identical construction and are secured to the base portion 47 by an eyelet which is formed at the base of each terminal and peaned over on the back side thereof. As shown in FIG. 2, the connections to the terminalpad 38 have not been made. It will be noted that the conductor tabs, only tabs 51, 52 of which are identified by reference numerals, are in the open position.

Having reference now to FIG. 3, I have shown therein the conductor tabs 51, 52 folded over to position coil conductor 17 in an overlying relation with terminal 42. Terminal 42 is formed with a lead window 53 which is provided to position the heavier wire leads. As will be hereinafter more fully described, an external lead in the illustrative embodiment of the invention may be inserted through the lead window 53 after the coil conductor 17 is soldered to the terminal 42. The lead window 53 is formed by bending the outer end of terminal 42 downwardly so that the lead window 53 is aligned with a connector tongue 54. The connector tongue 54 is cut out from the terminal 42 and extends downwardly to provide a gripping surface for one or more heavier leads, which maybe attached to terminal 42 in an underlying relation therewith. The fine coil conductor 17 is firmly engaged by conductor tabs 51, 52 in an overlying relation with terminal 42. Thus, the coil conductor 17 is firmly gripped before soldering. This provides the advantage that coil conductors, which are of extremely fine wire, particularly those brought out from a high voltage coil, are securely fastened to a terminal without need for twisting the leads about the terminal. Breakage of coil conductors resulting from such twisting is thereby eliminated. Furthermore, the location of the terminal pads 37, 38 at the ends of the magnetic core and coil assembly 5 eliminates the need for base insulation of the coils 30, 31. If required, base insulation may be provided over the ends of the magnetic core and coil assembly 5 where it will not impair the heat transfer from the coils 30, 31.

In FIG. 4, I have illustrated a modification of terminal 42 wherein only a single conductor tab 55 is cut out from the terminal 42 and a modification of the base portion 47.

In all other respects, the terminal 42 is identical in its construction to the terminal shown in FIG. 3. It will be noted that the base portion 47 has a T-shaped configuration. The corresponding parts of the terminal pad 38 are identified by the same reference numerals. In the terminal 42 shown in FIG. 4, coil conductor 17 is positioned in an overlying relation on terminal 42 by folding conductor tab 55 over the coil conductor 17 as illustrated therein.

Turning now to FIGS. 5 and 6, a magnetic coreand coil assembly 5 is shown with the coil conductors 9, 10, 11, 12, 13, 14, 1-5, 16, 17 and 18 positioned in their respective terminals. It will be seen that the coil conductors can be readily trimmed by providing a support means 56, 57 under the terminals and passing cutting blades 58, 59 downwardly along the ends of the terminals to cut off portions of the coil conductors 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18 which extend beyond the terminals. After the fine coil conductor leads are trimmed, the terminals are bent upwardly so that the terminal ends extend beyond the top sides of coils 30, 31 as is shown in FIG. 6. It will be seen that when the terminals are bent in this manner the terminals can be readily dip soldered.

Further, when the terminals are extended as shown in FIG. 6, they are not only positioned for soldering but when the soldering operation is completed they are in position for assembly with the heavier leads. A principal advantage of this feature of the terminal pad construction arrangement is that the bending, trimming and soldering operations are readily adaptable to mechanized techniques.

In FIG. 7, I have illustrated how all of the terminals of the magnetic core and coil assembly 5 can be simultaneously dip soldered. The magnetic core and coil assembly 5 in dashed outline shows the assembly 5 in position over a solder pot 60 containing molten solder 61. The magnetic core and coil assembly 5 is also shown in a lowered position. Since the-terminals of the terminal pads 37, 38 are accurately positioned with respect to magnetic core and coil assembly 5, the amount of immersion of the terminals in the solder can be readily controlled by bringing the yoke members 33, 34 in contact with a stop 62. It will be apparent, therefore, that the construction in accordance with the invention is readily adaptable to mechanized soldering operations.

Turning to FIGS. 8 and 9, I have illustrated therein an enlarged view of terminal 42. It will be seen that the stripped portion 64 of the external lead 29 is inserted into the lead window 53 until the end abuts against the connector tongue 54. The terminal 42 is then bent downwardly from the position shown in dashed outline in FIG. 9 until the end of the lead 29 is firmly gripped by the tongue 54 as shown therein. This arrangement provides the advantage that the lead 29 is precisely positioned on the magnetic core and coil assembly 5 so that it is possible to simultaneously solder this lead and all the others through the openings formed by cutting out the tongues. Even though the heavier lead 29 is disposed in an underlying relation with the terminal 42, the stripped portion 64 can be soldered from the top of the terminal 42 since the cutout portion provided by the tongue 54 exposes the end of the stripped portion 64.

Turning now to FIG. 10, the magnetic core and coil assembly 5 with the leads mechanically gripped and positioned on the terminals is shown therein. A soldering device having a plurality of electrodes 67, 68, 69, 70, 71, 72, 73, 74, 75 and 76 is shown being lowered in position over the terminals to simultaneously heat the heavy wire leads and provide solder to form a soldered connection between the heavier leads and the terminals.

From the foregoing description of the construction of the terminal pad arrangement for a magnetic core and coil assembly, it will be apparent that the connections with the coils and external leads can be made substantially in a horizontal plane level with the top side of the coils.

Hence, the terminal pads can be positioned so that they do not add to the over-all height of the magnetic core and coil assembly. Consequently, the case housing the magnetic core and coil assembly can be held within predetermined dimensional limits. Further, in the terminal pad arrangement in accordance with the invention both the top side and the bottom sides of the coils can be disposed near the ballast case so that heat generated by the coils during operation can be efliciently dissipated. For example, in a two-lamp forty-watt rapid start ballast magnetic core and coil assembly, it was possible to reduce the temperature as much as 3.6 degrees centigrade, as compared with an identical magnetic core and coil assembly employing a conventional terminal pad arrangement wherein the terminal pad was mounted on the top of the coils. Another advantage of the construction is that more eflicient electrical connections can be more economically eifected by either manual or mechanized assembly methods.

It will be understood that the specific embodiment of the invention which I have described herein is intended for illustrative purposes only and that the specific embodiment may be changed or varied without departing from the spirit and scope of the invention. While this invention has been explained by describing particular exemplifications thereof, it will be apparent that many modifications may be made. It is to be understood, therefore, that I intend by the appended claims to cover all such modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A ballast transformer comprising an elongate shunt type magnetic core having a pair of yoke members and a center winding leg, said yoke member being disposed at the side of said center winding leg to define coil receiving windows therein, said yoke members and center winding leg being formed of fiat laminations, a plurality of coils disposed on said center winding leg within said coil receiving windows and having a top side and a bottom side extending outwardly therefrom, means for joining said yoke members and center winding leg in assembled relation, said means joining said yoke members and center winding leg at the ends of the magnetic core, a first and a second terminal pad having a straight edge, each of said terminal pads having a base portion and a plurality of terminals, all of said terminals substantially aligned with said straight edge of the terminal pad, each of said terminals having at least one conductor tab cut out from said terminal, said tab extending from said terminal and folded over for retaining at least one conductor in position on said terminal in an overlying relation with said terminal, said base portion of said first terminal pad attached on said joining means at one end of the magnetic core attached on said joining means at the other end of the magnetic core, and a plurality of coil conductors brought out from said coils and connected in electrical engagement with said terminals.

2. The ballast transformer set forth in claim 1 wherein said outer end of reach of said terminals is formed with a lead receiving window extending in essentially perpendicular relation to said terminal and a connector tongue is cut from said terminal and textends at an acute angle with respect to said terminal, said connector tongue aligned with said lead receiving window for gripping the end of a lead brought out through said lead receiving window in an underlying relation with said terminal.

3. A terminal pad comprising a base portion formed of dielectric material, a plurality of terminals disposed adjacent to a straight edge thereof, each of said terminals extending from said base portion, said outer end of said terminals being formed with a lead receiving window extending in essentially perpendicular relation to said terminal, a connector tongue cut out from said terminal and extending at an acute angle with respect to said terminal, said connector tongue aligned with said lead receiving window and gripping an end of a lead brought out through said lead receiving window in an underlying relation with said terminal, at least one conductor tab cut out from said terminal, said tab extending fnom said terminal and folded over at least one conductor to retain said conductor in position on said terminal in an overlying relation with said terminal. 7

4. A terminal pad comprising a base portion formed of dielectric material and having a straight edge, a plurality of terminals extending along said straight edge, said terminals being formed of strips of conductive material and attached at one end to said base portion, the other end of each of said terminals having a lead receiving window portion extending in essentially perpendicular relation to the terminal, a tongue out out for said strip and aligned with said lead receiving window, portion and gripping the end of a lead inserted through said lead receiving window portion to retain the lead in position at the underside of said terminal, and at least one tab cutout from said terminal strip and extending from said terminal and engaging a coil conductor in position on the upper side of said terminal.

References Cited in the file of this patent UNITED STATES PATENTS 1,632,101 6/27 Thordarson 336-210 1,823,827 9/31 Franz 339-198 2,263,539 11/41 Grush 339275 2,992,370 7/61 Laviana 336192 3,146,419 8/64 Warrent et al., 336--192 FOREIGN PATENTS 1,018,703 1/53 France.

4/52 Great Britain.

JOHN F BURNS, Primary Examiner. 

1. A BALLAST TRANSFORMER COMPRISING AN ELONGATED SHUNT TYPE MAGNETIC CORE HAVING A PAIR OF YOKE MEMBERS AND A CENTER WINDING LEG, SAID YOKE MEMBER BEING DISPOSED AT THE SIDE OF SAID CENTER WINDING LEG TO DEFINE COIL RECEIVING WINDOWS THEREIN, SAID YOKE MEMBERS AND CENTER WINDING LEG BEING FORMED OF FLAT LAMINATIONS, A PLURALITY OF COILS DISPOSED ON SAID CENTER WINDING LEG WITHIN SAID COIL RECEIVING WINDOWS AND HAVING A TOP SIDE AND A BOTTOM SIDE EXTENDING WINDOWS AND HAVING A TOP SIDE AND A BOTTOM SAID YOKE MEMBERS AND CENTER WINDING LEG IN ASSEMBLED RELATION, SAID MEANS JOINED SAID YOKE MEMBERS AND CENTER WINDING LEG AT THE ENDS OF THE MAGNETIC CORE, A FIRST AND A SECOND TERMINAL PAD HAVING A STRAIGHT EDGE, EACH OF SAID TERMINAL PADS HAVING A BASE PORTION AND A PLURALITY OF TERMINALS, ALL OF SAID TERMINALS SUBSTANTIALLY ALIGNED WITH SAID STRAIGHT EDGE OF THE TERMINAL PAD, EACH OF SAID TERMINALS HAVING AT LEAST ONE CONDUCTOR TAB CUT OUT FROM SAID TERMINAL, SAID TAB EXTENDING FROM SAID TERMINAL AND FOLDED OVER FOR RETAINING AT LEAST ONE CONDUCTOR IN POSI- 